President Obama has frequently accused Republicans of blocking his agenda. His latest setbacks, however, have come at the hands of his fellow Democrats.

Liberals in Congress rejected Obama's preferred candidate to lead the Federal Reserve, former White House economic advisor Larry Summers, and opposed his call for military strikes to punish Syria for its alleged use of chemical weapons. Before that, 111 House Democrats refused to fund a National Security Agency surveillance program the administration said was essential.

The rebellion risks weakening Obama and his remaining allies in Congress as they head into showdowns with Republicans with a potential government shutdown, the debt ceiling, and the future of ObamaCare on the line. Why are so many Democrats breaking ranks at such a critical time?

One reason is that liberal Democrats, who rallied behind Obama in his first term, think it's time that he return the favor by consulting them more and getting more forceful in pushing the policies they believe in. Peter Baker and Jeremy W. Peters note at The New York Times that such defections are a common problem presidents face in their second terms.

With re-election behind him, members of his party see no need to stick with him to secure another four years. They are also looking ahead to the next election earlier than usual with the emergence of Hillary Rodham Clinton as a front-runner.

By the end of his fifth year, President Bill Clinton had alienated liberals with the North American Free Trade Agreement, a welfare overhaul and a balanced budget deal with Republicans. President George W. Bush in his fifth and sixth years was in worse shape with Republicans, who shelved his Social Security overhaul, rebelled against the deteriorating Iraq war and helped sink his Supreme Court nomination of Harriet E. Miers. [New York Times]

To some political strategists, the revolt by liberal Democrats against the potential nomination of Summers was the most telling of Obama's recent clashes with his fellow Democrats. Long-time GOP operative Dick Morris at The Hill says that act of defiance showed that Obama is losing power and becoming a lame duck, freeing Democrats who question his commitment to take him down a peg.

With increasing evidence that income inequality has flourished and widened under Obama, Democrats are impatient with his courting of Wall Street and his appointment of crony capitalists to key posts in Treasury and the Fed.

Under former President Clinton, 45 percent of all new personal income went to the top 1 percent. Under former President George W. Bush, it was 65 percent. So far under Obama, 95 percent of the income has gone to the richest 1 percent. [The Hill]

Strategists say Obama's handling of Syria, including his push for military strikes most Americans opposed, has also weakened his standing, although it's not the main reason for his troubles. Here's Kenneth T. Walsh at U.S. News & World Report:

More important is the decline in Americans' optimism about the economy, which is in turn eroding public confidence in Obama and his policies. "People are getting gloomier about the economy," says political scientist Bill Galston of the Brookings Institution, a former White House adviser to President Bill Clinton. "They don't see it getting better." And since that's the No. 1 issue, Obama is inevitably in a slump. [U.S. News]

Foes and friends alike, however, seem to believe that some of Obama's wounds are self-inflicted. John F. Harris and Todd S. Purdum at Politico say that something long viewed as one of Obama's strength — his ability to coolly and rationally consider all sides of an issue and find synthesis — has caused him to spout a "kaleidoscope" of options on matters such as Syria, making him come across as reluctant to lead and creating a power vacuum liberals were happy to fill.

Despite the perceived "contrast between Obama's campaign leaps and his governing lassitude," Maureen Dowd says at The New York Times, "Obama still has a secret weapon: Congressional Republicans, who might yet shut down the government or cause a cataclysmic default and make the president look good."

Of course, Obama still has all of the traits that have made him immensely popular with most Democrats, and won him two presidential elections. As Purdum and Harris note at Politico, Washington may be in "pile-on mode" now, but Obama can still turn things around with the intelligence, soaring oratory skills, and charm that have made him one of the most talented politicians of his generation. "No one will ever mistake Obama for warm and fuzzy," they say. "But when he tries even a bit, he can't help being winning."